SUMMARY
Idiopathic restrictive cardiomyopathy (IRC) is a rare form of heart muscle disease. Genetic studies have revealed that in about half the cases, IRC forms part of the hereditary sarcomeric contractile protein disease spectrum. Mutations in several sarcomere protein encoding genes are detected in 33-66% of cases. Among these, the mutations most commonly involve TNNI3 and MYH7. There is a disproportionately high incidence of TNNI3 mutations in patients with restrictive physiology. De novo mutations are also frequently seen in this group of patients. IRC and hypertrophic cardiomyopathy (HCM) with restrictive phenotype reflect the same or very similar disorders with different names due to arbitrary cut offs in the left ventricular wall thickness rather than two separate distinct diseases. HCM with restrictive physiology should be considered part of a continuous spectrum with IRC. This is because patients with HCM with restrictive phenotype bear far greater clinical and genetic resemblance to IRC than to rest of the HCM cohort.